1. Field of the Invention
The present invention relates to a method of determining both pressures and temperatures in a high temperature environment. The present invention also relates to a method of determining temperatures about a pressure-sensing element using a bi-functional heater. In addition, the present invention preferably relates to a pressure sensor with the pressure-sensing element and a heating element both integrated into the sensor's packaging, preferably onto the diaphragm of the pressure sensor, and particularly to such a pressure sensor capable of operating at high or elevated temperatures, and even more particularly to such a pressure sensor wherein the heating element is capable of both heating, at least in part, the pressure-sensing element and monitoring the temperature of the application area. Preferably, the pressure-sensing element is formed from shape memory alloy (SMA) materials that can be used at high or elevated temperatures as a pressure sensor with high sensitivity.
2. Technical Background
In recent years there has been a need for high or elevated temperature pressure sensors for various applications including for use in harsh environments. In these harsh environments such as for use in engine cylinders and turbine engines, the pressure sensors are exposed to corrosive, oxidizing environments, which put high mechanical and thermal stresses on the sensors. Various approaches have been taken in order to protect the pressure sensors from these environmental conditions and to allow the sensor to remain operational over extended periods of time. These approaches include sealing the pressure sensor to shield it from the environment.
While sealing the sensor from the environment has helped create a more durable sensor, at high temperatures these sensing devices also suffer from the drawback of having too low of a gage factor resulting in sensors with larger diaphragms or sensors with signals that are difficult to measure. Gage factor is a measure of the sensitivity of the sensor. With too low of a gage factor, the sensitivity of the sensing element is reduced creating difficulty in reading the sensing element, or the diaphragm size has to be increased to make up for the reduced sensitivity. These sensors are typically manufactured by diffusing the sensing elements into a silicon diaphragm. With these types of sensors the gage factor significantly decreases with increasing temperature. Another drawback of these types of sensors is that the sensor is subjected to thermal variations at the point of application of the sensing element resulting in proportionally large variations in the signals received from the sensor. Both these drawbacks have been addressed by providing a means of cooling these types of sensors in order to maintain a higher level of sensitivity or gauge factor, and less variability. Cooling the sensor, however, is not desirable because of the cost, complexity and space requirements for such devices. Cooling the sensor further sets up a large temperature gradient between the sensing device and the application environment, causing additional problems.
What is needed is a pressure sensor with a high sensitivity at elevated temperatures that is constructed to reduce or eliminate thermal variations about the sensing element at the point of application. What is also needed is a pressure-sensing device that can further monitor application temperatures. It is therefore the object of the present invention to provide a high temperature pressure sensor without the drawbacks of the prior art. It is further an object of the present invention to provide a method of determining both pressures and temperatures of a high temperature environment. It is still further the object of the present invention to provide a high temperature pressure sensor with an integrated heating element on the diaphragm to help eliminate thermal variations at the point of application. It is still further an object of the present invention to provide a pressure sensor with an integrated bi-functional heating element. It is still further the object of the present invention to provide a pressure sensor with a smaller sized diaphragm with an integrated heating element on the diaphragm, which is also capable of reading higher pressures. It is still further the object of the present invention to provide a heating element, which can be used to measure the temperature of the application area, as well as to control itself. Finally, it is even still further the object of the present invention to provide a high temperature sensor made from a shape memory alloy (SMA) material with a heating element integrated into the packaging.